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The aim of this study is to ensure the structural integrity of 90° back-to-back (B2B) pipe bends by developing a closed-form numerical solution for estimating the collapse load of shape distorted 90° B2B pipe bends using non-linear finite element (FE) analysis.

The collapse behaviour of 90° B2B pipe bends with ovality (C_o) and thinning (C_t) has been evaluated by non-linear FE approach. Moment load is applied in the form of in-plane closing moment (IPCM). The current FE approach was evaluated by the numerical solution for the plastic collapse moment of pipe bends, which has been published in the literature. The collapse moments were obtained from the twice elastic slope (TES) method using the moment-rotation curve of every individual model.

The implication of C_t/C_th on collapse load is found to be highly insignificant in terms of increasing bend radius and C_o. C_o weakens the geometry, and its effect on the collapse load is substantial. A closed-form numerical solution has been proposed to calculate the collapse load of 90° B2B pipe bend with shape imperfections.

The implications of shape distortion (C_o and C_t) in the failure analysis (collapse load) of 90° B2B pipe bends has not been investigated and reported.

The purpose of this paper is to quantify the combined effect of shape distortion and bend angle on the collapse loads of pipe bends exposed to internal pressure and in-plane closing bending moment. Non-linear finite element analysis with large displacement theory was performed considering the pipe bend material to be elastic perfectly plastic.

One half of the pipe bend model was built in ABAQUS. Shape distortion, namely, ovality (Co) and thinning (Ct), were each varied from 0% to 20% in steps of 5% and bend angle was varied from 30° to 180° in steps of 30°.

The findings show that ovality has a significant impact on collapse load. The effect of ovality decreases with an increase in bend angle for small thickness. The opposite effect was observed for large thickness pipe bends. The influence of ovality was more for higher bend angles. Ovality impact was almost negligible at certain internal pressure denoted as nullifying point (NP). The latter increased with an increase in pipe bend thickness and decreased with increase in pipe bend radius. For small bend angles one NP was observed where ovality impact is negligible and beyond this point the ovality effect increased. Two NPs were observed for large bend angles and ovality effect was maximum between the two NPs. Thinning yielded a minimal effect on collapse load except for small bend angles and bend radii. The influence of internal pressure on thinning was also negligible.

Influence of shape distortions and bend angle on collapse load of pipe bend exposed to internal pressure and in-plane closing bending has been not revealed in existing literature.

The purpose of this study is to investigate the effect of structural deformations and bend angle on plastic collapse load of pipe bends under an in-plane closing bending moment (IPCM). A large strain formulation of three-dimensional non-linear finite element analysis was performed using an elastic perfectly plastic material. A unified mathematical solution was proposed to estimate the collapse load of pipe bends subjected to IPCM for the considered range of bend characteristics.

ABAQUS was used to create one half of the pipe bend model due to its symmetry on the longitudinal axis. Structural deformations, i.e. ovality (C_o) and thinning (C_t) varied from 0% to 20% in 5% steps while the bend angle (ø) varied from 30° to 180° in steps of 30°.

The plastic collapse load decreases as the bend angle increase for all pipe bend models. A remarkable effect on the collapse load was observed for bend angles between 30° and 120° beyond which a decline was noticed. Ovality had a significant effect on the collapse load with this effect decreasing as the bend angle increased. The combined effect of thinning and bend angle was minimal for the considered models and the maximum per cent variation in collapse load was 5.76% for small bend angles and bend radius pipe bends and less than 2% for other cases.

The effect of structural deformations and bend angle on collapse load of pipe bends exposed to IPCM has been not studied in the existing literature.